1. Technical Field
This invention relates to the formation of an erosion resistant tip on an electrode, for example on one or both electrodes of a spark plug for use in an internal combustion engine; to an electrode having a tip formed by this process and to a spark plug in which either one or both electrodes are provided with tips formed in accordance with this process.
2. Description of the Prior Art
In order to achieve greater spark plug life and/or to allow the area of the electrode to be reduced to produce more efficient ignition, it is desirable to place and the electrode tips an erosion resistant material One suitable material is platinum, but any material which is more resistant to chemical erosion than Inconel may be used. Inconel is the conventional material used for spark plug electrodes and the name Inconel is a Registered Trade mark.
It is known from U.S. Pat. No. 4 810 220 to apply the platinum or other erosion resistant material using a sphere which is welded onto the respective base electrodes. However these spheres are necessarily of small size and therefore difficult to handle. Similar methods using platinum discs rather than spheres are also known. It is also known from U.S. Pat. No. 4 705 486 to weld a strip of platinum ribbon to the electrode.
In all these methods, it has proved difficult to ensure the necessary penetration of the platinum metal into the substrate to ensure that the platinum tip remains in place under service conditions.